Sheathed fiberglass heater wire

ABSTRACT

An apparatus is disclosed. The apparatus includes a resistive wire having a circumference. The apparatus further includes a first fiberglass layer disposed about the circumference of the resistive wire and along a length of the resistive wire. The apparatus further includes a second fiberglass layer. The apparatus further includes a third fiberglass layer, the second fiberglass layer disposed between the first fiberglass layer and the third fiberglass layer, the third fiberglass layer forming an outer layer and surrounding the second fiberglass layer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Application No. 15/880,417,filed Jan. 25, 2018, entitled “Sheathed Fiberglass Heater Wire,” thecontents of which is fully incorporated by reference in its entirety.

TECHNICAL FIELD

The subject matter described herein relates to a heater apparatus usedin electric appliances such as a refrigerator.

BACKGROUND

A variety of electrical appliances may incorporate a heating apparatusto prevent frost from forming, to evaporate moisture, to preventfreezing of components, etc. For example, a refrigerator often includesa freezer compartment, a refrigerator compartment, and a coolingportion. The cooling portion may provide cold air, via circulation of arefrigerant, to the freezer and refrigerator compartments. The coolingportion may also include one or more heaters to help manage temperatureof the different compartments, defrost components or compartments,prevent freezing, etc.

Additionally, the refrigerator may include various electrical componentssuch as various temperature sensors for detecting temperatures ofvarious compartments provided in the refrigerator and detectingcompletion of defrosting, a fan that blows air to the respectivecompartments, and a damper for adjusting the amount of cold air blow arearranged in the refrigerator. These electrical components can beconnected to a control substrate set up inside or outside therefrigerator via lead wires.

In some systems, the heater wires and/or lead wires may be exposed to aleaked refrigerant. Typical refrigerants have a relatively low ignitionpoint and are flammable. Often heater wires and/or lead wires mayoperate at a surface temperature that could surpass the ignition pointof the leaked refrigerant. Accordingly, it may be beneficial forimproved heater wires and/or lead wires that maintain a low surfacetemperature.

SUMMARY

Apparatus, systems and methods for controlling the temperature of aheating element are disclosed.

In a first aspect, an apparatus includes a resistive wire having acircumference. The apparatus further includes a first fiberglass layerdisposed about the circumference of the resistive wire and along alength of the resistive wire. The apparatus further includes a secondfiberglass layer. The apparatus further includes a third fiberglasslayer. The second fiberglass layer is disposed between the firstfiberglass layer and the third fiberglass layer. The third fiberglasslayer forms an outer layer and surrounds the second fiberglass layer.

In an interrelated aspect, a method is disclosed. The method includesproviding a heater wire disposed within a tube of a refrigerationsystem. The heater wire includes a resistive wire having acircumference. The heater wire further includes a first fiberglass layerdisposed about the circumference of the resistive wire and along alength of the resistive wire. The heater wire further includes a secondfiberglass layer. The heater wire further includes a third fiberglasslayer, the second fiberglass layer disposed between the first fiberglasslayer and the third fiberglass layer, the third fiberglass layer formingan outer layer and surrounding the second fiberglass layer. The methodfurther includes providing a current through the resistive wire to heatat least a portion of the refrigeration system.

In some variations one or more of the following features can optionallybe included in any feasible combination. The apparatus or heater wiremay also include a fiberglass core, the resistive wire wound about thefiberglass core. The first fiberglass layer can comprise an S-glass typefiberglass. The apparatus or heater wire may also include a polyimidelayer, the polyimide layer forming an outer layer and surrounding thethird fiberglass layer.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims. While certain features of the currently disclosed subject matterare described for illustrative purposes in relation to particularimplementations, it should be readily understood that such features arenot intended to be limiting. The claims that follow this disclosure areintended to define the scope of the protected subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, show certain aspects of the subject matterdisclosed herein and, together with the description, help explain someof the principles associated with the disclosed implementations. In thedrawings,

FIG. 1 is a cross-sectional diagram illustrating an exemplary embodimentof a heater wire, in accordance with certain aspects of the presentdisclosure;

FIG. 2 is a side view of the heater wire, in accordance with certainaspects of the present disclosure;

FIG. 3 is a cross-sectional diagram illustrating an exemplary embodimentof a heater wire, in accordance with certain aspects of the presentdisclosure;

FIG. 4A is a schematic diagram of an exemplary embodiment of a heaterwire and a lead wire, in accordance with certain aspects of the presentdisclosure;

FIG. 4B is a cross-sectional diagram illustrating an exemplaryembodiment of a heater wire, in accordance with certain aspects of thepresent disclosure;

FIG. 5 is schematic diagram of an exemplary embodiment of a heater wireand a lead wire, in accordance with certain aspects of the presentdisclosure; and

FIG. 6 is schematic diagram of an exemplary embodiment of a heater wireand a lead wire, in accordance with certain aspects of the presentdisclosure.

DETAILED DESCRIPTION

Appliance systems, like refrigerators, often incorporate heaters tocontrol temperatures within the appliance system. For example, it may bedesirable for the refrigerator to incorporate heaters to regulatetemperature in various compartments to prevent unwanted freezing,condensation, or frost accumulation. The heaters may radiate heat fromheater wires which receive power/current from lead wires within therefrigerator system. Often these wires may be placed near tubes orcomponents that contain flammable refrigerants.

In the conventional systems, however, the surface temperature of tubeshousing the heater and/or lead wires may increase during operation. Insome cases, it is possible that the surface temperature rises high,possibly exceeding the ignition point of the flammable refrigerant. Forexample, refrigerant R600a (Isobutane) has an ignition temperature of460° C. Hence, when the flammable refrigerant is used, it is beneficialthat the heater/lead wires, and tubes containing the wires, never be asource of ignition of leaked refrigerants due to supply of power throughthe wires. Common insulation tubes used for the heater/lead wiresinclude neoprene or double wall heat shrink tubing. Embodimentsdescribed herein relate to improved systems and wire configurations thatwould reduce the threat of ignition in such cases.

For example, it may be beneficial to design a system where the surfacetemperature of parts that may be exposed to a leaked refrigerant may notexceed the ignition temperature of the refrigerant (e.g., 460° C. forR600a) reduced by 100° C. (e.g., 360° C.). In some aspects, the systemmay be designed such that a maximum working surface temperature does notexceed 300° C. for the heater. Additionally, the system and theheating/lead wires may also have to comply with other requirements(e.g., energy efficiency requirements or size constraints). In somecases, the heater/lead wires may be configured to withstand a surge testprocedure or satisfy other tests required for certification, approval,etc.

FIG. 1 is a cross-sectional diagram illustrating an exemplary embodimentof a heater wire 100 for use in a refrigeration system, in accordancewith certain aspects of the present disclosure. As shown in FIG. 1 , theheater wire 100 comprises a fiberglass core 102, a resistive wire 104wound around the fiberglass core 102, a first fiberglass layer 106, asecond fiberglass layer 108, and a third fiberglass layer 110. Asillustrated, the first fiberglass layer 106 is located between theresistive wire 104 and the second fiberglass layer 108, the secondfiberglass layer 108 is located between the first fiberglass layer 106and the third fiberglass layer 110, and the third fiberglass layer 110is the outer layer with its inner surface coupled to the secondfiberglass layer 108. While three fiberglass layers are shown in FIG. 1, more or fewer fiberglass layers are also possible. For example, theheater wire 100 can comprise four or five fiberglass layers to increasea total diameter of the heater wire 100. In some aspects, the heaterwire 100 may also be used as a lead wire. In some implementations, theresistive wire 104 may comprise a nickel-chromium wire (e.g., 80-20NiCr), any iron, copper, or aluminum-based wire alloy , or any othersuitable resistive wire. In some aspects, the resistive wire 104 cancomprise a single or double resistance wire. In other aspects, theresistive wire 104 can comprise three or more wires.

In some aspects, the fiberglass material used for the fiberglass core102 and the fiberglass layers 106, 108, and 110 may comprise the same ordifferent fiberglass material. For example, the fiberglass core 102 andthe first fiberglass layer 106 may comprise a first fiberglass materialand the second and third fiberglass layers 108 and 110 may comprise asecond fiberglass material. Additionally, each of the fiberglass core102 and the fiberglass layers 106, 108, and 110 may comprise differentfiberglass material, or any combination of fiberglass material. In someembodiments, the fiberglass material may comprise an S-glass typefiberglass.

FIG. 2 is a side view of the heater wire 100, in accordance with certainaspects of the present disclosure. As shown in FIG. 2 , the resistivewire 104 wrapped around the fiberglass core 102 may have a firstdiameter θ₁ and the entire heater wire 100 and the third fiberglasslayer may have a second diameter θ₂. The second diameter θ₂ larger thanthe first diameter θ₁. In some aspects, the second diameter θ₂ comprisea diameter of 3.8-3.9 mm. In some embodiments the second diameter θ₂ mayconfigured to fit within a tube of the refrigerator or refrigerationsystem.

The heater wire 100 configuration may allow improved safety andperformance within a refrigeration system. The heater wire 100 mayexhibit increased ability to withstand high voltages compared toconventional heater wires. For example, the heater wire 100 may beconfigured to withstand a high potential (HIPOT) of up to 1500 V.Additionally, the heater wire 100 may also withstand a surge test at2000 V without failure. The heater wire 100 may also exhibit reducedleakage current and greater insulation resistance compared toconventional heater wires. In some aspects, the heater wire 100 can beconfigured to exhibit a leakage current of less than 0.07 mA. The heaterwire 100 can also exhibit an insulation resistance of greater than 2 GΩ.Such properties demonstrate an improved performance of heater wires usedwithin conventional refrigeration systems.

FIG. 3 is a cross-sectional diagram illustrating an exemplary embodimentof a heater wire 300 for use in a refrigeration system, in accordancewith certain aspects of the present disclosure. As shown in FIG. 3 , theheater wire 300 comprises a fiberglass core 302, a resistive wire 304wound around the fiberglass core 302, a first fiberglass layer 306, asecond fiberglass layer 308, a third fiberglass layer 310, and apolyimide layer 312.

As illustrated, the first fiberglass layer 306 is located between theresistive wire 304 and the second fiberglass layer 308, the secondfiberglass layer 308 is located between the first fiberglass layer 306and the third fiberglass layer 310, the third fiberglass layer 310 islocated between the second fiberglass layer 308 and the polyimide layer312, and the polyimide layer 312 is the outer layer of the heater wire300 with its inner surface in contact with the third fiberglass layer310. In some aspects, the heater wire 300 may also be used as a leadwire. In some embodiments, one or more of the fiberglass core 302,resistive wire 304, first fiberglass layer 306, second fiberglass layer308, third fiberglass layer 310 may comprise the same or differentmaterial as the fiberglass core 102, resistive wire 104, and thefiberglass layers 106, 108, and 110 of the heater wire 100 of FIG. 1 .While two fiberglass layers are shown in FIG. 3 , other numbers offiberglass layers are also possible. For example, the heater wire 300can comprise three or more fiberglass layers to increase a totaldiameter of the heater wire 300.

In some implementations, the polyimide layer 312 may comprise a tape ofa polyimide film and silicone adhesive that is designed for hightemperature masking applications, including the protection of printedcircuit board gold finger contacts during wave soldering. The polyimidelayer 312 may beneficially increase the dielectric insulation capabilityof the heater and the heater wire 300. This may also increase theprotection against unsafe failure during operation. In someimplementations, the polyimide layer 312 can comprise one or morelayers. For example, the polyimide layer 312 can comprise two or morepolyimide layer which can increase the total diameter of the heater wire300.

For example, the heater wire 300 may exhibit increased ability towithstand high voltages compared to conventional heater wires and theheater wire 100. In some aspects, the heater wire 300 can be configuredto withstand a surge test at 4000 V without failure. The heater wire 300may also exhibit reduced leakage current and greater insulationresistance compared to conventional heater wires and the heater wire100.

In some aspects, the heater wires 100 and/or 300 are implemented in arefrigeration system. While embodiments described below apply to theheater wire 300, they may also apply to the heater wire 100. In therefrigeration system, the heater wire 300 may be connected to a powersupply through lead wires. In some aspects, the power supply maycomprise a battery, a wall power outlet, or another voltage/currentsupply. In some aspects, the heater wire 300 may be disposed within atube of the refrigeration system. The tube may comprise a stainlesssteel tube, neoprene tube, a double wall heat shrink tube, a fiberglasstube, a glass tube, or any other suitable tubing.

As the power supply provides current through the heater wire 300, theheater wire 300 generates heat. A portion of that heat can betransferred to the tubing surrounding the heater wire 300, and thesurface of the tubing can rise to a temperature less than the ignitionpoint of the flammable refrigerant, thereby defrosting the peripheralparts. In some aspects, the heater wire 300 may also be configured toprovide heat to evaporate moisture within the refrigeration systemprevent frost from forming, and/or to prevent freezing of components ofthe refrigeration system.

In the event of a flammable refrigerant leaking in an area around theheater wire 300, the configuration of the heater wire 300 maybeneficially keep the surface temperature of the heater wire 300, andany tube containing the heater wire 300, below the ignition point of theflammable refrigerant. As noted above, in some aspects, the heater wire300 may be configured to have a maximum surface temperature at least100° C. below the ignition point of the refrigerant. Hence, even ifthere is flammable refrigerant around the heater wire 300, accidents dueto surface temperatures exceeding the ignition point can be prevented.

In some implementations, the heater wire 300 may be coupled with a leadwire 400 at an end 350 of the heater wire 300. For example, the end 350of the heater wire 300 may be coupled with the lead wire as shown inFIGS. 4A and 4B, within a seal 402, such as a neoprene seal. As theheater wire 300 is coupled with the lead wire 400 at the end of theheater wire 300, outside of the tubing surrounding the heater wire 300,one or more (e.g., two, three or more) lead wires may contact an end ofthe resistive wire 304, or extend alonga length of the heater wire 300..The lead wires 400 supply current to the resistive wire 304 of theheater wire 300 by contacting at least a portion of the heater wire 300,such as at each of the winds of the restive wire 304, or an end of theresistive wire 304.

In some implementations, an unheated or reduced temperature zone (e.g.,a cold zone) may be desired along an end portion (e.g., the end 350) ofthe heater wire 300 at or along a portion of the heater wire 300 thatconnects with the lead wire 400. The cold zone may be desired to reducethe likelihood of a fire, break in connection, overheating of thejunction between the heater wire and the lead wire, and the like. Toform the cold zone, one or more wires 320 (e.g., metal wires) may extendalong the fiberglass core 302 and contact a portion of the resistivewire 304, such as at the winds of the resistive wire coil (see, e.g.,FIG. 4B). The contact between the wires 320 and the resistive wire 304creates a short circuit, limiting or reducing the temperature at theregions of contact. In some implementations, the wires 350 may separatefrom the resistive wire 304, as the wires 350 may become entangled withthe fibers of the fiberglass core 302. Thus, it may be beneficial forthe lead wires 400 to be crimped directly to the resistive wire 304.

Directly coupling the lead wire 400 with the resistive wire 304 can helpto ensure that any desired cold zones along the heater wire 300 remainat the desired temperature, and may help to reduce the length of thecold zone. For example, the lead wire 400 may be coupled with theresistive wire 304 over the regions where the cold zone is desired (seeFIGS. 5 and 6 ), at or adjacent to an end of the cold zone, where it isdesired for the heater wire to be heated. This configuration helps toensure that the heat caused by the resistive wire 304 does not pass tothe cold zone of the heater wire 300, so that the temperature of thecold zone of the heater wire 300 remains below the ignition point of theleaked refrigerant, for example.

FIGS. 5 and 6 illustrate examples of the lead wires 400 crimped directlyto the resistive wire 304, consistent with implementations of thecurrent subject matter. For example, FIG. 5 illustrates an example ofthe lead wire 400 directly coupled with the resistive wire 304. Here,the lead wire 400 may not contact the fiberglass core 302. FIG. 6illustrates an example of the lead wire 400 directly coupled with theresistive wire 304, and at least a portion of the fiberglass of theheater wire 300 (e.g., the fibers of the fiberglass core 302). Couplingthe lead wire 400 with the resistive wire 304 and fibers of thefiberglass material may help to strengthen the junction between the leadwire 400 and the heater wire 300. The lead wires 400 may includeneoprene or other materials. The direct connection between the resistivewire 304 and the lead wires 400 help to maintain consistent contactbetween the lead wires 400 and the resistive wire 304.

As shown in FIGS. 5 and 6 , the lead wire 400 is coupled with theresistive wire 304 within the heater wire 300, and external to the seal(e.g., neoprene seal). Thus, the thickness and/or circumference of theneoprene seal may be reduced. The heater wire 300 may also be moreeasily be assembled, and be implemented in other heating applicationsthat have limited available space and thus may require a reduced sealsize or reduced overall wire circumference. In some implementations inwhich the heater wire 300 is coupled with the lead wire 400 within theseal 402 and external to the heater wire 300, the seal may not bewell-formed, or may crack, exposing the junction between the heater wire300 and the lead wire 400. Exposing the junction between the heater wire300 and the lead wire 400 may allow unwanted humidity to develop aroundthe resistive wire 304 or undesirably increase the likelihood of a fire,or a break in the connection between the lead wire 400 and the heaterwire 300. Thus, coupling the lead wire 400 with the resistive wire 304within the heater wire (e.g., within the tube surrounding the heaterwire) and adjacent to or external to the seal 402 may provide anenhanced boundary to limit or prevent humidity from entering the heaterwire 300. Furthermore, the material of the lead wire 400 (e.g.,neoprene) may vulcanize with the material of the seal 402 (e.g.,neoprene) to enhance the sealing effect.

In some implementations, the connection between the heater wire 300 andthe lead wire 400 is insulated using an isolation material 406. Theisolation material 406 may be designed for high temperature maskingapplications, including the protection of printed circuit board goldfinger contacts during wave soldering. The isolation material mayinclude polyimide (which may include a tape of a polyimide film andsilicone adhesive), fiberglass, a combination of polyimide tape andfiberglass tape, and the like.

A person skilled in the art will appreciate that, while the methods,systems, and devices are disclosed herein for heater and/or lead wiresin a refrigeration system, the methods, systems, and devices can be usedin a variety of other electrical appliances, components, and systems.

In the descriptions above and in the claims, phrases such as “at leastone of” or “one or more of” may occur followed by a conjunctive list ofelements or features. The term “and/or” may also occur in a list of twoor more elements or features. Unless otherwise implicitly or explicitlycontradicted by the context in which it used, such a phrase is intendedto mean any of the listed elements or features individually or any ofthe recited elements or features in combination with any of the otherrecited elements or features. For example, the phrases “at least one ofA and B;” “one or more of A and B;” and “A and/or B” are each intendedto mean “A alone, B alone, or A and B together.” A similarinterpretation is also intended for lists including three or more items.For example, the phrases “at least one of A, B, and C;” “one or more ofA, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, Balone, C alone, A and B together, A and C together, B and C together, orA and B and C together.” Use of the term “based on,” above and in theclaims is intended to mean, “based at least in part on,” such that anunrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems,apparatus, methods, computer programs and/or articles depending on thedesired configuration. Any methods or the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. The implementations set forth in the foregoing description donot represent all implementations consistent with the subject matterdescribed herein. Instead, they are merely some examples consistent withaspects related to the described subject matter. Although a fewvariations have been described in detail above, other modifications oradditions are possible. In particular, further features and/orvariations can be provided in addition to those set forth herein. Theimplementations described above can be directed to various combinationsand subcombinations of the disclosed features and/or combinations andsubcombinations of further features noted above. Furthermore, abovedescribed advantages are not intended to limit the application of anyissued claims to processes and structures accomplishing any or all ofthe advantages.

Additionally, section headings shall not limit or characterize theinvention(s) set out in any claims that may issue from this disclosure.Specifically, and by way of example, although the headings refer to a“Technical Field,” such claims should not be limited by the languagechosen under this heading to describe the so-called technical field.Further, the description of a technology in the “Background” is not tobe construed as an admission that technology is prior art to anyinvention(s) in this disclosure. Neither is the “Summary” to beconsidered as a characterization of the invention(s) set forth in issuedclaims. Furthermore, any reference to this disclosure in general or useof the word “invention” in the singular is not intended to imply anylimitation on the scope of the claims set forth below. Multipleinventions may be set forth according to the limitations of the multipleclaims issuing from this disclosure, and such claims accordingly definethe invention(s), and their equivalents, that are protected thereby.

1-18. (canceled)
 19. An apparatus comprising: a resistive wire having acircumference; a first fiberglass layer disposed about the circumferenceof the resistive wire and along a length of the resistive wire; a secondfiberglass layer; a third fiberglass layer, the second fiberglass layerdisposed between the first fiberglass layer and the third fiberglasslayer, the third fiberglass layer forming an outer layer and surroundingthe second fiberglass layer; a lead wire crimped onto the resistivewire, thereby reducing tangling of the resistive wire and the lead wirewith one or more of the first fiberglass layer, the second fiberglasslayer, and the third fiberglass layer, the lead wire configured tosupply a current to the resistive wire; and a cold zone defined at leastin part by a portion of the lead wire and a portion of the resistivewire, the cold zone formed by a short circuit created when one or moremetal wires contact at least the portion of the resistive wire.
 20. Theapparatus of claim 19, further comprising a fiberglass core, theresistive wire wound about the fiberglass core.
 21. The apparatus ofclaim 19, wherein the first fiberglass layer comprises an S-glass typefiberglass.
 22. The apparatus of claim 19, wherein the first fiberglasslayer comprises a fiberglass material different than a fiberglassmaterial of the second fiberglass layer.
 23. The apparatus of claim 20,wherein the fiberglass core comprises an S-glass type fiberglass. 24.The apparatus of claim 19, wherein the third fiberglass layer comprisesa fiberglass material different than the first fiberglass layer anddifferent than the second fiberglass layer.
 25. The apparatus of claim19, further comprising a polyimide layer, the polyimide layer forming anouter layer and surrounding the third fiberglass layer.
 26. Theapparatus of claim 25, wherein the polyimide layer comprises a polyimidefilm and silicone adhesive.
 27. The apparatus of claim 19, wherein theresistive wire, the first fiberglass layer, the second fiberglass layer,and the third fiberglass layer form at least a part of a heater wire,the heater wire configured to be disposed within a tube of arefrigeration system; and wherein the cold zone is configured to preventignition of a refrigerant of the refrigeration system.
 28. A methodcomprising: providing a heater wire disposed within a tube of arefrigeration system, the heater wire comprising: a resistive wirehaving a circumference; a first fiberglass layer disposed about thecircumference of the resistive wire and along a length of the resistivewire; a second fiberglass layer; a third fiberglass layer, the secondfiberglass layer disposed between the first fiberglass layer and thethird fiberglass layer, the third fiberglass layer forming an outerlayer and surrounding the second fiberglass layer; a lead wire crimpedonto the resistive wire, thereby reducing tangling of the resistive wireand the lead wire with one or more of the first fiberglass layer, thesecond fiberglass layer, and the third fiberglass layer, the lead wireconfigured to supply a current to the resistive wire; and a cold zonedefined at least in part by a portion of the lead wire and a portion ofthe resistive wire, the cold zone formed by a short circuit created whenone or more metal wires contact at least the portion of the resistivewire; and providing a current through the resistive wire to heat atleast a portion of the refrigeration system.
 29. The method of claim 28,wherein the heater wire further comprises a fiberglass core, theresistive wire wound about the fiberglass core.
 30. The method of claim28, wherein the first fiberglass layer comprises an S-glass typefiberglass.
 31. The method of claim 28, wherein the first fiberglasslayer comprises a fiberglass material different than a fiberglassmaterial of the second fiberglass layer.
 32. The method of claim 29,wherein the fiberglass core comprises an S-glass type fiberglass. 33.The method of claim 28, wherein the third fiberglass layer comprises afiberglass material different than the first fiberglass layer anddifferent than the second fiberglass layer.
 34. The method of claim 28,wherein the heater wire further comprises a polyimide layer, thepolyimide layer forming an outer layer and surrounding the thirdfiberglass layer.
 35. The method of claim 34, wherein the polyimidelayer comprises a polyimide film and silicone adhesive.
 36. The methodof claim 28, wherein the cold zone is configured to prevent ignition ofa refrigerant of the refrigeration system.
 37. The method of claim 36,wherein the cold zone is positioned adjacent to a junction between thelead wire and the resistive wire, wherein the lead wire is crimped ontothe resistive wire at the junction.